PRELIMINARY
CYW43340
3.4 External 32.768 kHz Low-Power Oscillator
The CYW43340 uses a secondary low frequency clock for low-power-mode timing. Either the internal low-precision LPO or an external
32.768 kHz precision oscillator is required. The internal LPO frequency range is approximately 33 kHz ± 30% over process, voltage,
and temperature, which is adequate for some applications. However, a trade-off caused by this wide LPO tolerance is a small current
consumption increase during WLAN power save mode that is incurred by the need to wake up earlier to avoid missing beacons.
Whenever possible, the preferred approach for WLAN is to use a precision external 32.768 kHz clock that meets the requirements
listed in Table 4.
Note: BT operations require the use of an external LPO that meets the requirements listed in Table 4.
Table 4. External 32.768 kHz Sleep Clock Specifications
Parameter
Nominal input frequency
LPO Clock
Units
kHz
32.768
±200
Frequency accuracy
Duty cycle
ppm
30–70
%
Input signal amplitude
200–1800
mV, p-p
–
Signal type
Square-wave or sine-wave
Input impedancea
>100k
<5
Ω
pF
Clock jitter (during initial start-up)
<10,000
ppm
a.When power is applied or switched off.
Document Number: 002-14943 Rev. *L
Page 14 of 96
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